Filter for the sorption of components of tobacco smoke which are harmful to health

ABSTRACT

A filter for sorption of components of tobacco smoke which are harmful to health comprises ceramic particles bonded to form a porous structure (12). In order to avoid contamination within a short period of time even when the filter is not properly disposed of, and without causing a loss in sorption or in the smoking sensation, the filter has decreasing water solubility from a tobacco-side portion (1) to an opposite mouth-side portion (2).

FIELD OF THE INVENTION

The invention relates to a filter for sorption of components of tobaccosmoke which are harmful to health, comprising ceramic particles bondedto form a porous structure.

DESCRIPTION OF THE PRIOR ART

Cigarette filters are used to remove harmful substances from tobaccosmoke. Conventional filters are made of cellulose acetate, a plasticthat is difficult to biodegrade.

This has the disadvantage that improperly disposed of cigarette buttscause considerable environmental pollution and animals can be harmed ifthey ingest the cigarette butt.

To circumvent this circumstance, alternative materials for filters havebeen developed. U.S. Pat. No. 2,996,067 describes a filter for thesorption of harmful substances made of ceramic particles bonded to forma porous structure. Although ceramic particles are essentially naturallyoccurring inorganic substances that are unproblematic in comparison withvarious types of plastic, the problem nevertheless remains that suchfilters lead to pollution if they are not disposed of properly.

Filters made of hemp and cotton, for example, are therefore known fromU.S. Pat. No. 2,996,067.

Although such filters are biodegradable, such biodegradation processesrequire several days for complete degradation and an appropriateenvironment for the microorganisms responsible for the degradation,which, however, is not prevalent, especially in urban areas.

Other filters comprising ceramic particles are disclosed in EP0539191A1,EP0766929A2, US3428054A and GB1243358A. GB1005786A and EP0539191A1disclose filters comprising ceramic particles bonded to form a porousstructure. EP1504682A1 and KR200476478Y1 disclose manufacturingprocesses of conventional cigarette filters.

SUMMARY OF THE INVENTION

The invention is thus based on the object of proposing a filter of thetype described at the beginning, which avoids contamination within ashort time even in the case of improper disposal, without causing lossesin terms of sorption properties and smoke sensation.

The invention solves the problem posed in such a way that the filter hasa decreasing water solubility from a tobacco-side portion to an oppositemouth-side portion. As a result of this measure, the filter dissolves oncontact with larger quantities of water, for example rain. Undesirabledissolution of the filter upon contact with saliva during smoking isprevented in such a way that the water solubility decreases toward themouth-side portion of the filter, whereby the filter maintains itssorptive capacity along the entire length of the filter during smoking.For example, it may be provided that the mouth-side portion will havepoor or no water solubility. The change in water solubility may besectional or continuous. The mouth-side portion may thereby comprise theend of the filter that is enclosed by the mouth of a smoker. Thetobacco-side portion may comprise the end of the filter that is adjacentto the tobacco of the cigarette.

In order to be able to set the required water solubility of the filterwithout requiring a complex production process, it is proposed that theceramic particles are bound with a water-soluble binder, the massproportion of which increases from the tobacco-side portion to theopposite mouth-side portion of the filter. On contact with largerquantities of water, the binder goes into solution and the insolubleceramic particles are carried away by the water as suspended solids orsediment as non-toxic inorganic substances. In principle, the watersolubility can be reduced by increasing the mass fraction of the binder,so that the section of the filter with the lower mass fraction of thebinder is dissolved first when it comes into contact with largerquantities of water. Starch, for example, can be used as a water-solublebinder.

Particularly simple manufacturing conditions with sufficientlydifferentiated water solubility of the filter are achieved if the filtercomprises at least three portions with mutually different and in eachcase constant binder content. This means that a substantially constantbinder content is provided within a portion. The portion on the mouthside has the highest binder content and the portion on the tobacco sidehas the lowest binder content. The binder content of the middle portionlies between the binder contents of the other two portions.

In order for the filter to completely disintegrate during weak rainshowers and still be resistant to large amounts of saliva duringsmoking, the binder content in the tobacco-side portion can be in arange of 1-2 wt %, in at least one middle portion in a range of 2-3 wt%, and in the mouth-side portion in a range of 3-4 wt %. With thiscomposition, the filter does not dissolve even when smoked for aparticularly long time. However, if it comes into contact with largeramounts of water, rapid dissolution of the binder occurs. With thiscomposition, a filter according to the invention with conventionalcigarette filter dimensions requires about 20 seconds to be completelydissolved in a cup filled with water and equipped with a stirring rodset at 150 revolutions per minute.

In order to enable the filter to bind the toxic substances reliablywithout negatively affecting the degradability of the filter and thesmoking sensation, it is proposed that the porosity of the filterincreases from the tobacco-side portion to the opposite mouth-sideportion. Due to the lower porosity of the filter in the tobacco-sideportion, there is a larger effective surface area for binding the toxicsubstances. The further the tobacco smoke flows toward the mouth-sideportion, the less toxic substances it has due to sorption in thetobacco-side portion, so that the porosity can increase in favor oflow-resistance draw of the smoker, or the effective surface area candecrease, without exposing the smoker to the risk of overexposure totoxic substances. The greater porosity and thus lower stability at themouth-side portion of the filter, which after all has a lower watersolubility, also has the positive effect that it can be pulverized in asimple manner, for example by a pressure load, whereby even themouth-side portion, which is more difficult to dissolve with water, canbe dissolved without residue. Due to the porous structure of the filter,however, not only can a desired binding of harmful substances takeplace, but in addition the water required for degradation can penetrate,thus accelerating the degradation process. Porosity is the ratio of voidvolume to total volume of the filter.

In order that the porosity can be adjusted in the same process step asthe water solubility and with the same accuracy, it is advisable in aparticularly easy-to-manufacture embodiment of the device according tothe invention for the filter to have at least three portions withdifferent and in each case constant porosity. The tobacco-side portionhas the lowest porosity and the mouth-side portion has the highestporosity. The porosity of the middle portion lies between the porositiesof the other two portions.

It has been found that the filter according to the invention achievessimilar properties in terms of sorption of harmful substances fromtobacco smoke and in terms of smoke sensation when the porosity in thetobacco-side portion is in a range of 35-50%, in the middle portion in arange of 50-65% and in the mouth-side portion in a range of 65-80%. Theproposed porosity in the tobacco-side portion in the range of 35-50%provides enough effective surface area to bind even the highconcentration of harmful substances in the filter. Porosity in the rangeof 65-80% in the mouth-side portion causes lower flow resistance for thealready almost completely detoxified tobacco smoke and also allows easypulverization by external forces. Porosity in the range of 50-65% in themiddle portion represents a compromise between effective surface areaand low flow resistance.

The filter according to the invention can be manufactured in a methodaccording to the invention, wherein successively differing mixturescomprising ceramic particles, placeholder particles and water-solublebinder are filled into a mold, whereupon the mold contents are pressedand heated to decompose the placeholder particles and form the porousstructure of bound ceramic particles. The mixtures may differ from eachother in terms of binder content, such that the mixture for forming themouth-side portion of the filter has a larger binder content than themixture for forming the tobacco-side portion of the filter. The mixturesmay also differ with respect to the placeholder particle content orplaceholder particle size distribution, such that the mixture forforming the mouth-side portion of the filter after decomposition of theplace-holder particles has a greater porosity than the mixture forforming the tobacco-side portion of the filter after decomposition ofthe placeholder particles. For example, NH₄HCO₃ can be used as theplaceholder particle, which is decomposed into NH₃, H₂O and CO₂ by heattreatment and outgases to form the porous structure.

To give a smoker a pleasant mouthfeel when smoking, the elasticity ofthe filter can decrease inward in the radial direction. Due to the moreelastic and therefore more bendable nature at the outer shell of thecigarette filter, a haptic sensation similar to conventional cigarettefilters can be created. The radial progression of elasticity can becontinuous, but also discrete. Particularly simple conditions forimproving the haptic mouthfeel result when felted ceramic fibers areprovided as the outer filter shell layer.

It has been found that the mouthfeel can be further positivelyinfluenced if the porosity of the filter increases radially outward froma filter core to a filter shell. Due to the lower porosity in the filtercore, a sufficiently effective surface for binding the toxic substancescan be achieved. Due to the increasing porosity in the direction of thefilter shell, the texture of a conventional cigarette filter can bemimicked. The higher porosity at the outer filter shell has the furtheradvantage that water needed for degradation can penetrate into thefilter core, thus accelerating the degradation process. Naturally, themixture for the filter shell must be selected so that it cannot bedegraded by a smoker's saliva during the smoking process. In principle,however, the change in porosity can also take place continuously indiscrete steps.

A possible embodiment of a porosity changing in radial direction can beachieved if at least one intermediate portion is provided between afilter core portion with a predetermined placeholder particle fractionand a filter shell portion surrounding the filter core with a higherplaceholder particle fraction, the placeholder particle fraction ofwhich lies between the placeholder particle fractions of the filter coreportion and filter shell portion. Filter core portion, intermediateportion and filter shell portion can mean portions extending in theaxial direction of the filter which occupy only part or the entirelength of the filter. It is thus conceivable that the porosity variescontinuously or in discrete portions in both the axial direction and theradial direction.

A filter according to the invention can be produced by means of a devicehaving a continuous casting mold which has inlet channels downstream ofwhich a heating unit and a separating device are arranged in the castingdirection, wherein at least two inlet channels for the continuouscasting mold are provided which extend into one another at a distanceand are arranged coaxially with respect to one another and with respectto the continuous casting mold. Since the inlet channels extend into oneanother at a distance according to the invention, a filter can beproduced with a filter core having different material properties thanthe outer filter shell when the inlet channels are fed with differentmixtures, as a result of which a porosity and/or water solubility thatvaries in the radial direction of the filter can be set. Due to thedistance between the inlet channels extending into each other, themixtures differing from each other can be introduced into the continuouscasting mold through the free spaces created between the inlet channelwalls. It is recommended that each inlet channel is fed with a differentcompound, so that the composition of the filter can be changed by addingor removing certain inlet channels.

In principle, therefore, the device can also be used to set a porosityand/or water solubility that varies in the axial direction of the filterif, for example, the continuous casting mold is first filled with afirst mixture through only one inlet channel and then filled with asecond mixture that differs from the first mixture through another inletchannel. Another way to control the filter composition changing in theradial or axial direction is when the mixtures enter the continuouscasting mold from the inlet channels at different inlet speeds. In orderto achieve a homogeneous transition at the boundary layers between themixtures drawn from the inlet channels despite a desired watersolubility gradient or a desired varying porosity, it is proposed thatthe inlet channels with a larger diameter project beyond the inletchannels with a smaller diameter in the casting direction. In this way,the inlet channels with the larger diameter in each case span a mixingarea in which the mixtures can mix at their transition areas. Favorabledesign conditions arise when the inlet channel with the largest diameterforms the continuous casting mold.

In order to increase the production throughput of the filters accordingto the invention, several continuous casting molds extending parallel toone another can be arranged to form a continuous casting module andseveral continuous casting modules can be arranged on a common basebody, wherein the base body has a heating unit for all continuouscasting molds and a rotor blade extending between the heating unit andthe continuous casting molds as a separating device. In this way, theproduction process is parallelized. Due to the arrangement of thecontinuous casting modules on a common base body, one heating unit andone rotor blade can be used for all continuous casting molds, resultingin a particularly energy-saving production process.

The device according to the invention can be used to carry out a methodfor the continuous production of a filter for the sorption of tobaccosmoke. According to the invention, mixtures differing from one anotherand comprising ceramic particles, place-holder particles andwater-soluble binder are first introduced into the continuous castingmold through at least two inlet channels extending at a distance intoone another and arranged coaxially to one another and to a continuouscasting mold, wherein the inlet velocities of the mixtures differingfrom one another in the respective inlet channels are varied in theradial and/or axial direction of the filter to adjust the watersolubility and/or the porosity, and thereafter the continuous castingmold contents are fractionated and heated to decompose the placeholderparticles and form the porous structure of bound ceramic particles. Forexample, if a filter is to be produced with water solubility decreasingfrom a tobacco-side portion to an opposite mouth-side portion, one inletchannel may be charged with a mixture having a high binder content andanother inlet channel may be charged with a mixture having a lowerbinder content. To produce an end with lower water solubility, the inletspeed of the inlet channel with the mixture with a high binder contentis first increased, while the inlet speed of the inlet channel with themixture with a lower binder content is 0 or selected to be lower. If thewater solubility of the filter is now to decrease in the axialdirection, the inlet velocity of the inlet channel with the mixture witha high binder content is reduced and the inlet velocity of the inletchannel with the mixture with a lower binder content is increased. Theinlet channels extending into each other also allow the mixtures to belayered one inside the other, which makes it possible to adjust thewater solubility in the radial direction as well. By arranging the inletchannels and varying the inlet velocities, it is therefore possible toadjust the water solubility both in the axial direction and in theradial direction. The same naturally applies to the porosity. If, forexample, the porosity of the filter is to increase radially outward froma filter core to a filter shell, the inner inlet channel can be chargedwith a mixture with a smaller proportion of placeholder particles orwith a smaller placeholder particle size distribution, and the outerinlet channel with a mixture with a larger proportion of placeholderparticles or placeholder particle size distribution. After thisadjustment of the composition of the continuous casting mold content, itis fractionated by a separating device and then heated.

BRIEF DESCRIPTION OF THE INVENTION

In the drawing, the subject matter of the invention is shown by way ofexample, wherein:

FIG. 1 shows a filter according to the invention for sorption of tobaccosmoke in a first embodiment,

FIG. 2 shows a schematic section along line II-II of FIG. 1 ,

FIG. 3 shows a schematic representation of a device for carrying out themethod according to the invention for filling three mixtures in a firstembodiment,

FIG. 4 shows a schematic representation of a device for carrying out themethod according to the invention for pressing and heating in a firstembodiment,

FIG. 5 shows a schematic cross-section of a second embodiment of afilter according to the invention,

FIG. 6 shows a partial exploded view of a device according to theinvention for producing a filter according to the invention in a secondembodiment, and

FIG. 7 shows a schematic section through a continuous casting module ofthe device shown in FIG. 6 on an enlarged scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A filter for sorption of tobacco smoke according to the invention shownin FIG. 1 has a tobacco-side portion 1 and a mouth-side portion 2. Inorder for the filter to be degraded by larger amounts of water, but notby the saliva of a smoker, the water solubility of the filter decreasesfrom the tobacco-side portion 1 to the mouth-side portion 2.

This can be achieved in a particularly simple manner if the ceramicparticles are bonded with a water-soluble binder 3, the mass fraction ofwhich increases from the tobacco-side portion 1 to the oppositemouth-side portion of the filter 2.

As can be seen from FIG. 1 , the increase in the mass fraction of thebinder 3 can take place portion by portion, with the mouth-side portion2 having the largest binder fraction and the tobacco-side portion 1having the lowest binder fraction. The binder content of the middleportion 4 is therefore between the binder content of the tobacco-sideportion 1 and the mouth-side portion 2. The binder content within therespective portions 1, 2, 4 is constant.

A particularly well-degradable filter results if the binder content inthe tobacco-side portion 1 is in a range of 1-2 wt %, in the middleportion 4 in a range of 2-3 wt % and in the mouth-side portion 2 in arange of 3-4 wt %.

As can be seen from FIG. 2 , the porosity can increase from thetobacco-side portion 1 to the mouth-side portion 2. The low porosity ofthe tobacco-side portion 1 results in a particularly large effectivesurface area, which means that even high concentrations of harmfulsubstances from the tobacco smoke can be bound. The concentration oftoxic substances therefore decreases in the direction of the mouth-sideportion 2, which means that a higher porosity can be provided there infavor of lower flow losses.

The increase in porosity can also take place portion by portion,analogously to the binder content. The mouth-side portion 2 has thehighest porosity and the tobacco-side portion 1 the lowest porosity.Consequently, the porosity of the middle portion 4 lies between theporosity of the tobacco-side portion 1 and the mouth-side portion 2. Theporosity within the respective portions 1, 2, 4 is constant.

Effective binding of toxic substances without giving the smoker anunfamiliar smoking sensation is achieved when the porosity in thetobacco-side portion 1 is in a range of 35-50%, in the middle portion 4in a range of 50-65%, and in the mouth-side portion 2 in a range of65-80%.

FIGS. 3 and 4 refer to a method for manufacturing the filter accordingto the invention. As shown in FIG. 3 , first a first mixture 5 a isfilled into a mold 6. Whereupon a second mixture 5 b and third mixture 5c are filled into the mold 6. Between filling of the different mixtures5 a, 5 b, 5 c, any dump cone 7 formed during filling can be leveled.This can be carried out, for example, by a vibrating plate 8. Themixtures 5 a, 5 b, 5 c comprise ceramic particles, placeholder particlesand water-soluble binder, wherein for each mixture 5 a, 5 b, 5 c thebinder fraction and/or the placeholder particle fraction and/or theplaceholder particle size distribution can vary. In the exemplaryembodiment shown in FIG. 2 , mixture 5 a has the largest binder fractionand, to produce a large porosity, placeholder particles with the largestparticle size distribution. Accordingly, mixture 5 a is intended to formthe mouth-side portion 2. Mixture 5 b has both a lower binder fractionand placeholder particles with a smaller particle size distribution thanmixture 5 a and is thus intended for the middle portion 4. Mixture 5 chas the lowest binder fraction and placeholder particles with the lowestparticle size distribution and is provided for forming the tobacco-sideportion 1. Obviously, the layering of mixtures 5 a, 5 b, 5 c can also bedone in reverse order. A method with more than three mixtures can alsobe provided if a more differentiated design of porosity or watersolubility is desired. Preferably, the particle size distribution of theplaceholder particles can range from 15 to 300 nm. However, variation ofthe porosity can also be achieved by changing the mass fraction of theplaceholder particles while maintaining the same particle sizedistribution.

After filling, as can be seen from FIG. 4 , the layered mixtures 5 a, 5b, 5 c are pressed together by, for example, a ram 9 and heated by aheating unit 10. Due to the applied heat, the placeholder particles, forexample NH₄HCO₃, are transferred to the gas phase as NH₃, H₂O and CO₂,thereby leaving gaps 11 in the porous structure 12, as disclosed in FIG.2 .

FIG. 5 shows a second embodiment of a filter according to the invention,in which the elasticity decreases inwardly. Furthermore, the filter hasa decreasing water solubility from a tobacco-side portion 1 to anopposite mouth-side portion 2. The radial inward decrease in elasticitycan be achieved in a simple manner by providing an elastic, mattedceramic fiber layer 13. Another possibility is when the porosity, i.e.the volume of the gaps 11 of the filter increases radially outward froma filter core 14 to a filter shell 15.

The increase in porosity in the radial direction outward can be discretein that at least one intermediate portion 18 is provided between afilter core portion 16 having a predetermined placeholder particlefraction and a filter shell portion 17 surrounding the filter core 14and having a higher placeholder particle fraction, the placeholderparticle fraction of which lies between the placeholder particlefractions of the filter core portion 16 and filter shell portion 17.

FIG. 6 shows a device according to the invention for producing a filteraccording to the invention with continuous casting molds 19, downstreamof which in the casting direction 20 are a separating device 21 and aheating unit 10. As can be seen from FIG. 7 , each continuous castingmold 19 has inlet channels 22 which extend into one another at adistance, i.e. with the formation of an intermediate channel between theshell inner surface of the outer inlet channel 22 and the shell outersurface of the inner inlet channel 22. The continuous casting mold 19may thus form the inlet channel 22 with the largest tube diameter. Theinlet channels 22 can be flow-connected via different supply channels24, which supply the inlet channels 22 with different mixtures viapumps, for example.

For improved mixing of mixtures conveyed through the different inletchannels 22 and to adjust material properties that vary in the axialdirection, the larger diameter inlet channels 22 may project beyond thesmaller diameter inlet channels 22 in the casting direction 20.

A plurality of continuous casting molds 19 extending parallel to eachother may be combined to form a continuous casting module 25. Asdisclosed in FIG. 6 , a plurality of continuous casting modules 25 canadvantageously be arranged on a base body 26, wherein the base body 26has apertures 27 corresponding to the continuous casting molds 19 forguiding the continuous casting mold contents or the heated filter. Inthis regard, the base body 26 has a common heating unit 10 for allcontinuous casting molds 19 and a rotor blade extending between theheating unit 10 and the continuous casting molds 19 as a separatingdevice 21. The base body 26 may also have a heat sink 28.

After adjusting the filter composition in the continuous casting mold 19via the inlet channels 22, the continuous casting mold contents areforced through the apertures 27. During the pushing through, thecontinuous casting mold content is fractionated by a separating deviceand then heated and hardened by a heating unit 10. Subsequently, acooling step can be provided by a heat sink 28.

1. A filter for sorption of components of tobacco smoke that are harmfulto health, said filter comprising: ceramic particles bonded to form aporous structure; wherein the filter has decreasing water solubilityfrom a tobacco-side portion to an opposite mouth-side portion.
 2. Thefilter according to claim 1, wherein the ceramic particles are bondedwith a water-soluble binder, the water-soluble binder having a massfraction that increases from the tobacco-side portion to the oppositemouth-side portion of the filter.
 3. The filter according to claim 2,wherein the filter further comprises a third portion, said tobacco-sideportion, said mouth-side portion, and the third portion each having arespective different and constant binder content.
 4. The filteraccording to claim 3, wherein the third portion comprises at least onemiddle portion, and the binder content in the tobacco-side portion is ina range of 1-2 wt %, in the at least one middle portion in a range of2-3 wt %, and in the mouth-side portion in a range of 3-4 wt %.
 5. Thefilter according to claim 1, wherein the filter has a porosity thatincreases from the tobacco-side portion to the opposite mouth-sideportion.
 6. The filter according to claim 5, wherein the filter furtherhas a third portion, said tobacco-side portion, said mouth-side portion,and the third portion each having a respective porosity that differsfrom the porosities of the other portions and is constant in saidportion.
 7. The filter according to claim 6, wherein the third portioncomprises at least one middle portion, and the porosity in thetobacco-side portion is in a range of 35-50%, in the middle portion in arange of 50-65% and in the mouth-side portion (23 in a range of 65-80%.8. The filter according to claim 1, wherein the filter has an elasticitythat decreases inwardly in a radial direction of the filter.
 9. Thefilter according to claim 1, wherein the filter has a porosity thatincreases radially outwardly from a filter core to a filter shell of thefilter.
 10. The filter according to claim 9, wherein at least oneintermediate portion (18) is supported between a filter core portionhaving a predetermined placeholder particle fraction and a filter shellportion surrounding the filter core and having a placeholder particlefraction higher than the predetermined placeholder particle fraction,wherein the placeholder particle fraction of said intermediate portionlies between the placeholder particle fractions of the filter coreportion and the filter shell portion.
 11. A method for producing afilter for sorption of tobacco smoke, said method comprising: fillingsuccessively mutually different mixtures comprising ceramic particles,placeholder particles and water-soluble binder into a mold; and pressingand heating contents of the mold so as to decompose the place-holderparticles and to bond the ceramic particles so as to form a porousstructure.
 12. A device for producing a filter according to claim 1,comprising a continuous casting mold that has inlet channels; and aheating unit and a separating device supported downstream of said inletchannels in a casting direction, a heating unit and a separating device;wherein the continuous casting mold has characterized in that at leasttwo inlet channels that extend at a distance into one another and arearranged coaxially with respect to one another and with respect to thecontinuous casting mold.
 13. The device according to claim 12, whereinwherein some of the inlet channels have a larger diameter and some ofthe inlet channels have a smaller diameter, wherein the inlet channelswith the larger diameter project beyond the inlet channels with thesmaller diameter in the casting direction.
 14. The device according toclaim 13, wherein the continuous casting mold is one of a plurality ofcontinuous casting molds extending parallel to one another that areformed into a continuous casting module, and said continuous castingmodule is one of a plurality of continuous casting modules that arearranged on a common base body, wherein the base body supports theheating unit and the separating unit comprises a rotor blade extendingbetween the heating unit and the continuous casting molds.
 15. A methodfor the continuous production of a filter for the sorption of tobaccosmoke, said method comprising: initially introducing mixtures differingfrom one another and comprising ceramic particles, placeholder particlesand water-soluble binder into a continuous casting mold through at leasttwo inlet channels that extend into one another at a distance and arearranged coaxially with one another and with respect to the continuouscasting mold; varying inlet velocities of the mixtures differing fromone another in the respective inlet channels in a radial and/or axialdirection of the filter so as to adjust water solubility and/or theporosity of the filter, and then fractionating and heating thecontinuous casting mold contents are so as to decompose the placeholderparticles and bind the ceramic particles so as to form the porousstructure of said bound ceramic particles.
 16. The filter according toclaim 4, wherein the filter has a porosity that increases from thetobacco-side portion to the opposite mouth-side portion, and saidtobacco-side portion, said mouth-side portion, and the third portioneach have a respective porosity that differs from the porosities of theother portions, wherein the porosity in the tobacco-side portion is in arange of 35-50%, in the middle portion in a range of 50-65% and in themouth-side portion in a range of 65-80%.
 17. The filter according toclaim 16, wherein the filter has an elasticity that decreases inwardlyin a radial direction of the filter, and a porosity that increasesradially outwardly from a filter core to a filter shell of the filter.18. The filter according to claim 17, wherein at least one intermediateportion is supported between a filter core portion having apredetermined placeholder particle fraction and a filter shell portionsurrounding the filter core and having a placeholder particle fractionhigher than the predetermined placeholder particle fraction, wherein theplaceholder particle fraction of said intermediate portion lies betweenthe placeholder particle fractions of the filter core portion and thefilter shell portion.